During which changes of state do atoms that cannot move past one another become free to move

The correct answer is from solid to liquid (melting), and from liquid to gas (sublimation).

Explanation:

In the solid-state the energy of the molecules is low, so the molecules will have very little movement. In the liquid state, molecules have a higher level of energy, and as they move from solid to liquid state they acquire greater mobility. In a gaseous state, the energy level is very high and the molecules have a higher degree of mobility.

This can also be described through the predominant molecular forces in each state. The cohesion forces present in solids are stronger than those of repulsion. In the liquid state, the repulsion and attraction forces are balanced. Finally, in the gaseous state, the repulsive forces between the molecules predominate.  

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